saved words and browsing questions

Hello, please help if you know the answer to my three questions, thanks.
1. If you accidentally save a word as acceptable, but don't mean to, is there a way to undo it? Example: I accidentally accepted "tje" as a word, when trying to type "the."
2. Is there a way to not get periods automatically entered if you double space?
3. When broswing, is there a way to quit the browser without just hitting back a bunch? I know you can hit home and get out, but I mean a way to close the application, besides using advanced task killer.